Does shining a flashlight behind your knee prevent jet lag?

October 5, 2001

Dear Cecil:

Is there any medical or scientific evidence for the practice of preventing jet lag after long plane rides by placing a lighted flashlight behind one's knees just prior to landing? I read a short piece in an airline magazine a few years ago and finally got around to trying it on two long plane trips--to and from the eastern Mediterranean and to and from New Zealand. It worked. I had no jet lag and fell into normal wake/sleep cycles in those time zones. But friends say I experienced a psychological placebo.

— Gene Wojciechowski, Richmond, New Hampshire

It's possible. It's also possible you experienced a few too many of those little bottles of Seagram's (although, to be honest, excessive alcohol is said to exacerbate jet lag, not prevent it). I personally think this business about shining a light behind your knee is a crock. But you know what? Maybe it's not.

First let's get the facts straight. Nobody except a few screwballs claims that merely sticking a flashlight behind your knee will prevent jet lag. It makes a good yarn, though, which explains how one Les Adams (no relation) managed to get himself quoted in jet lag stories by the Wall Street Journal and ABC's 20/20. All you had to do, Adams said, was strap a Maglite to your leg and let it shine into the crease behind your knee for an unspecified time. He planned to market a "Jet Lag Lite" for those would couldn't master the art of flashlight-strapping on their own.

This ticked off researchers Scott Campbell and Patricia Murphy at Cornell University, who claimed Adams had gotten the idea from a study they'd published and accused him of violating patent rights. Their research showed that a light shone on the popliteal region (the back of the knee, for you civilians) could significantly advance or retard the body's circadian rhythms--that is, the normal fluctuations in body temperature and chemistry associated with the daily cycle of sleeping and waking.

Campbell and Murphy had put 15 volunteers in a lab for four days and at varying times during the second day had hooked them up to a knee light (not a flashlight but a fiber optic pad illuminated by a halogen lamp) for three hours. Meanwhile the researchers monitored the volunteers' body temperature and other indicators to determine the effect on circadian rhythms. Sure enough, they found that if the light pulse was administered before body temperature bottomed out (this typically occurs around 4 or 5 AM), the body rhythm was retarded three hours--that is, the temp hit bottom at 7 AM rather than 4 and was still doing so a couple days later. If the light pulse was administered after the low point, the rhythm was advanced a couple hours.

Why behind the knee? Because many blood vessels are close to the surface there. The researchers theorized that exposure to light caused changes in blood chemistry that reset the body's internal clock--an obvious benefit for those prone to jet lag.

The study was open to criticism on various grounds, most obviously the small numbers involved--just 15 subjects and 33 trials. No one, including the original investigators, has attempted to replicate the research, and Campbell concedes that his scientific peers consider his findings "an aberrant result." Even if the results pan out (no disrespect, but I'm not holding my breath), there's more involved than just strapping a light to your leg. You also need precise knowledge of your personal circadian rhythm so that you begin the light pulse at the right time and don't inadvertently set your body clock forward when you're trying to set it back.

For what it's worth, other people using completely different approaches--diet, pills, and what have you--say their methods are guaranteed to prevent jet lag too. Is the effect real or just a placebo? All I know is I've got a system that requires no gimmicks at all. When I traveled from the U.S. to Israel a couple years ago, a trip that involved an eight-hour time difference, I resisted the temptation to take a nap when I arrived (11 AM local time, 3 AM body time). Instead I stayed up till 9 PM local time and got a good night's sleep. Instant reset of my body clock, no loss of daylight hours, and no flashlight batteries to replace. And here's the kicker: it's the system Campbell uses too.